Method of scheduling data transmission in a radio network

ABSTRACT

In a method and apparatus for scheduling users in radio network system, the scheduling priority for each user of a group of users is made dependent on the unusable time for each user. Scheduling of the users is performed in accordance with the determined scheduling priority.

TECHNICAL FIELD

The present invention relates to a method and a device for schedulingdata transmission in a radio network.

BACKGROUND

Today a number of different technologies for cellular telecommunicationexist. One such existing cellular telecommunication technology isWideband Code Division Multiple Access (WCDMA).

In a WCDMA system, which is a powerful standard able to transmit dataover a radio network at very high speed, a User Equipment (UE) such as amobile telephone communicates over radio channels with base stationstypically denoted Node B. The omni-area around a base station can beallocated into several sectors known as cells. The base stationtransmits and receives signals over selected radio channels in eachcell. Typically, a base station is connected to one or more radionetwork controller nodes (RNC). One or more RNCs are, in turn, connectedto the core network (CN). The CN is usually connected, e.g., via agateway to other telecommunication networks, such as the public switchedtelephone network or to a packet-data network such as the internet.

In a wideband code division multiple access (WCDMA) mobiletelecommunications system, the information transmitted between a basestation and a particular UE is modulated by mathematical codes (such asspreading codes) to differentiate the information for different servicesof this UE and the information for different UEs which are utilizing thesame radio frequency. Thus, in WCDMA the data signal over each mobileradio employs its own unique code sequence to encode its signal. Thereceiver, knowing the code sequences of the mobile radio it services,decodes the received signal to recover data from each radio.

In the standard 3GPP Release. 5, High-Speed Downlink Packet Access(HSDPA) is introduced for WCDMA. HSDPA achieves the increase in the datatransfer speeds by defining a new WCDMA channel: a high-speed downlinkshared channel (HS-DSCH) that operates in a different way from existingDPCH channels and is used for downlink communications to the mobile.

Along with the HS-DSCH channel, three new physical channels are alsointroduced. One is the High Speed-Shared Control CHannel (HS-SCCH) whichinforms the user that data will be sent on the HS-DSCH 2 slots later.The second one is the uplink High Speed-Dedicated Physical ControlCHannel (HS-DPCCH), which carries acknowledgement information andcurrent channel quality indicator (CQI) of the user. This value is thenused by the Node-B in scheduling, including scheduling user andcalculating how much data to send to the scheduled UEs. The thirddownlink physical channel is the High Speed-Physical Dedicated SharedCHannel (HS-PDSCH), which carries the information transferred byHS-DSCH.

Furthermore, TTI, Transmission Time Interval, is a parameter in WCDMAand other digital telecommunication networks related to encapsulation ofdata from higher layers into frames for transmission on the radio linklayer. TTI refers to the length of an independently decodabletransmission on the radio link. The TTI is related to the size of thedata blocks passed from the higher network layers to the radio linklayer.

To combat errors due to fading and interference on the radio link thedata in the transmitter buffer is divided into blocks and then the bitswithin a block are encoded and interleaved. The length of time requiredto transmit one such block determines the TTI. At the receiver side allbits of a given block must be received before they can be deinterleavedand decoded.

In order to be able to adapt quickly to the changing conditions in theradio link a communications system must have shorter TTIs. In order tobenefit more from the effect of interleaving and to increase theefficiency of error-correction and compression techniques a system must,in general, have longer TTIs. These two contradicting requirementsdetermine the choice of the TTI.

In 3GPP Release '99 the shortest TTI is 10 ms and can be 20 ms, 40 ms,or 80 ms. In 3GPP Release-5 the TTI for HSDPA is reduced to 2 ms. Thisprovides the advantage of faster response to link conditions and allowsthe system to quickly schedule transmissions to mobiles whichtemporarily enjoy better than usual link conditions

In FIG. 1, the timing of HSDPA transmission in the air interface isdepicted. The control information for a UE is sent over the HS-SCCH 2slots prior to the corresponding data transmission over the HS-DSCH inorder to ensure that the UE has enough time to receive and decode thenecessary information. Based on this information the UE determines ifand how to receive the subsequent HS-DSCH data. If the UE determinesthat there is an HS-DSCH carrying data for that particular UE, the UEreceives the HS-DSCH data and starts to process the received data assoon as the HS-DSCH receiving ends.

The UE takes about 7.5 slots to process the received HS-DSCH. Then theacknowledgement information for the HS-DSCH is sent over the first slotof HS-DPCCH. The duration from the HS-SCCH transmission start to theHS-DPCCH transmission end is about 15.5 slots and can not beinterrupted, otherwise the data could be regarded as being lost.

In order to perform Inter Frequency Handover (IFHO) and Inter RadioAccess Technology Handover (IRAT HO), ComPressed Mode (CPM) for HSDPA isto be implemented. FIG. 2 shows the timing of the CPM timing in the airinterface. The CPM is defined in “3GPP TS 25.215 V6.4.0, TechnicalSpecification Group Radio Access Network; Physical layer-Measurements(FDD)”. The following abbreviations will be used: TG: Transmission Gap.TGPL: Transmission Gap Pattern Length in number of frames. TGCFN:Transmission Gap Connection Frame Number, which is the Connection FrameNumber (CFN) of the first radio frame of the first pattern within theTG-Pattern sequence. TGSN: Transmission Gap Starting Slot Number, whichindicates the time offset from the TGPL start to the transmission gapstart. TGL: Transmission Gap Length in number of slots. TGD:Transmission Gap start Distance in number slots, which is the durationbetween the starting slots of two consecutive transmission gaps withinone transmission gap pattern.

Furthermore, there are different TG-Patterns for different measurementtargets. Here are some examples:

The current default TG-Pattern for IFHO:

TGPL=4, TGL=7, TGSN=4, TGD=0, TGCFN=0

The current default TG-Patterns for IRAT HO:

TGPL=8, TGL=7, TGSN=4, TGD=0, TGCFN=0

TGPL=8, TGL=7, TGSN=4, TGD=0, TGCFN=2

TGPL=8, TGL=7, TGSN=4, TGD=0, TGCFN=6

There are also some proposed TG-Patterns namely:

TGPL=4, TGL=14, TGSN=8, TGD=0, TGCFN=0

TGPL=8, TGL=14, TGSN=8, TGD=0, TGCFN=0

TGPL=24, TGL=14, TGSN=8, TGD=0, TGCFN=4

TGPL=24, TGL=14, TGSN=8, TGD=0, TGCFN=12

TGPL=24, TGL=14, TGSN=8, TGD=0, TGCFN=20

During the TG, the UE is performing measurements in another frequency inthe original network or another network with different radio accesstechnology (RAT). Hence, the UE can not transmit signal to or receivethe signal from the original serving cell during this time.

The impact of the CPM on HSDPA users will now be described. As theprocess from the HS-SCCH transmission start to the correspondingHS-DPCCH transmission end can not be interrupted, scheduling a user inCPM should be avoided during a gap described above and the 15.5 slotsbefore the gap. For a 7-slot or 14-slot gap, the number of the usableslots is then about 22.5 or 29.5 slots. The UE may work in multipleTG-Patterns. Also, depending on the TGD setting, there are possiblyseveral gaps within one pattern.

Furthermore, the UE can be in CPM for several seconds or even longer,during which the UE suffers a longer packet delay than before the UEentered CPM.

Another factor that has to be considered is that the UE in CPM usuallysuffers very bad channel quality. For some schedulers such asproportional fair or maximum channel quality indicator (CQI), whichconsiders the channel quality, the scheduling delay for the UEs in CPMis very large even if the impact of the gap is not taken into account.

Hence, the UEs in CPM experience a very large packet delay compared tothose UEs not in the CPM due to both the bad channel quality and thetransmission gap. The UEs in CPM also have a high risk of experiencing ahigh packet loss because of the retransmission failure resulted from T1timer expires and the maximum scheduling delay reached if there is amaximum delay threshold setting in the scheduler such as the High SpeedMedium Access protocol (MAC-hs) delay scheduler.

SUMMARY

It is an object of the present invention to improve the performance in aradio system having users operating in different modes within the sameradio network.

It is another object of the present invention to overcome or at leastreduce some of the problems associated with schedulers, in particularschedulers for use in radio networks supporting CPM.

These objects and others are obtained by providing a scheduler operativeto take the unusable time for each user in group of users into accountin the scheduler to increase the satisfaction rate of these users.

Thus, in the case when the radio system supports CPM, by increasing thescheduling priority of the UE in CPM according to T_(unusable) duringT_(pre), the probability of the UE to be scheduled before the start ofT_(unusable) is increased. This will turn result in that a UE in CPMwill have an increased probability to send out the packets that isalready queued for a long time and process the retransmissions beforethe start of T_(unusable). Thus, the packet delay and the packet lossrate of the UEs in CPM is decreased.

Thus, by increasing the scheduling probability of the users in CPMbefore the unusable TTIs occurs, the impact from these unusable TTIs onthe packet delay and the packet loss rate of these UEs can be reduced.For the UEs with delay sensitive services over HSDPA, such packet delayreduction can increase their probability to be satisfied.

The inclusion of the unusable time for each user as a parameter whendetermining the scheduling priority will hence increase performance forthe overall system for CPM supporting systems as well as other systemswith the same or similar properties.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by way ofnon-limiting examples and with reference to the accompanying drawings,in which:

FIG. 1 is a view of the timing of HSDPA transmission in the airinterface

FIG. 2 is a view of the timing of the CPM timing in the air interface

FIG. 3 is a general view of a WCDMA system supporting HSPDA and CPM

FIG. 4 is a view illustrating timing in a scheduler adapted to considerunusable TTIs

FIGS. 5 a-5 c are flowcharts illustrating different steps performed in ascheduler adapted to consider unusable TTIs

DETAILED DESCRIPTION

FIG. 3 is a general view of a WCDMA system 300 supporting HSPDA and CPM.The system 300 comprises a base station (Node B) 301. The base station301 serves a number of mobile terminals, usually termed User Equipment(UE) 303, located within the area covered by the base station 301. Thebase station 101 is also connected to a radio network controller node(RNC) 305. The system 300 also comprises a scheduler 307 co-located withor an integral part of the base station 301. Some aspects of thescheduler 307 will be described more in detail below.

In order to reduce the negative impact of CPM for the UEs the system 300is configured to consider the impact of the unusable TTIs resulting fromthe gap in a certain period of time before the start of these unusableTTIs in the scheduling, for example the MAC-hs scheduling.

FIG. 4 illustrates an example when the scheduler considers the unusableTTIs in order to reduce the packet delay and packet loss rate for UEs inCPM. In FIG. 4 T_(unusable) denotes is the number of the unusable slotsresulted from one gap. Further, T_(pre) denotes the period of time thatshould consider T_(unusable) before the start of T_(unusable), and t₀ isthe start of T_(pre). By increasing the scheduling priority of the UE inCPM according to T_(unusable) during T_(pre), the probability of the UEto be scheduled before the start of T_(unusable) is increased, whichresults in that a UE in CPM will have an increased probability to sendout the packets that is already queued since long and process theretransmissions before the start of T_(unusable). As a result, thepacket delay and the packet loss rate of the UEs in CPM is decreased.

Below different examples on how to implement such an approach indifferent schedulers are described more closely:

Example 1 Implementation in a Delay Scheduler

Prior to each gap, during T_(pre), the coming unusable TTIs as is usedas the delay:

f(maximum_delay)=1/T _(MAX)−(t _(queue) +T _(unusable)))

where t_(queue) is the time corresponding to the time the packet hasalready been queued, T_(MAX) is the maximum allowable queuing delay andT_(pre) is determined by the scheduler and the delay requirements ofdifferent services.

Example 2 Implementation in a Proportional Fair Scheduler

Prior to each gap, during T_(pre), take the coming unusable TTIs as theused time:

${f({average\_ rate})} = \left( \frac{N_{b}}{t_{used} + T_{unusable}} \right)^{- 1}$

where t_(used) is a certain period before the scheduling prioritycalculation, N_(b) is the number of transmitted bits during the timet_(used) and T_(pre), is determined by the scheduler and the delayrequirements of different services.

Example 3 Adding a New Priority Coefficient in Existing Schedulers

In addition to all the existing priority coefficients, during T_(pre), anew priority coefficient, a pattern coefficient, is added for the usersin CPM:

f(TG_Pattern)=TGPL_(max)*5/(TGPL_(max)*5−T _(unusable)/3), TGPL in frame(10 ms) unit, T_(unusable) in slot unit.

Where T_(pre) can be set as the number of HSDPA usable TTIs between thecurrent gap and the last gap. If there is just one TG-Pattern for a UEin CPM, T_(unusable) can be set the sum of the unusable TTIs within onepattern of the TG-Pattern sequence and TGPL_(max) is the TGPL of thisTG-Pattern. If there are multiple TG-Patterns time multiplexed for a UEin CPM, TGPL_(max) is the largest TGPL of these TG-Patterns andT_(unusable) can be set as the sum of the unusable TTIs from all ofthese TG-Patterns within one pattern of the TG-Pattern sequence with thelargest TGPL.

Below some examples illustrating how the scheduling coefficients asdescribed above can be used when determining the scheduling priority.

For a proportional scheduler,

scheduling priority=f(average_rate)*f(CQI)

*f(retrans)*f(TG_Pattern)

where f(average_rate) is the scheduling coefficient of average rate,f(CQI) is the scheduling coefficient of CQI and f(retrans) is thescheduling coefficient of retransmission.

For a delay scheduler,

scheduling priority=f(maximum_delay)*f(CQI)

f(retrans)*f(TG_Pattern)

where f(maximum_delay) is the scheduling coefficient of maximum delay.Also, for all schedulers adapted to determine the scheduling prioritybased on many different scheduling coefficients different schedulingcoefficients may be given different weights when determining thescheduling priority. Hence, in the case when the scheduler has access tomany parameters representing a number of different schedulingcoefficients, the scheduling priority can be determined as a function ofall or some of those parameters depending on the environment in whichthe scheduler is deployed.

From a feasibility perspective, since the Node B and the UE aretriggered usually 1˜2 s before they enter the CPM simultaneously, thereis enough time for the Node B to configure the scheduler in advance.

In FIGS. 5 a-5 c, different steps performed in a scheduler operating inaccordance with the principles set out above are described in moredetail.

In FIG. 5 a, a flow chart illustrating steps performed in a scheduler,for example a MAC-hs, scheduler adapted to operate in accordance withthe scheduling methods as described herein is shown. First thescheduling starts in a step 501. Next the scheduler obtains informationabout a first user in a user pool, step 503 Thereupon the schedulingpriority for that particular user is calculated in a step 505. Thecalculations performed in step 505 can for example be any of thecalculations described above for obtaining a scheduling priority. Forall users in the pool the steps 503 and 505 are then repeated asindicated by step 507. When all users have been assigned a schedulingpriority, the scheduler then schedules the users in accordance withtheir determined priorities, step 509.

In FIG. 5 b, a flow chart illustrating some other steps performed in ascheduler, for example a MAC-hs scheduler, adapted to operate inaccordance with the scheduling methods as described herein is shown.Thus, the scheduler 307 can at any time receive a signal from the RNC305 that a particular UE 303 will enter CPM as indicated by step 511.Upon reception of such a signal for a particular UE the scheduler willcheck if that particular UE is associated with delay sensitive servicesprovided by HSDPA, step 513. If the particular UE is associated withdelay sensitive services provided by HSDPA, the scheduler will bereconfigured, for example by updating the scheduler priority calculationalgorithm for that particular UE, to reflect the changed mode of the UE,step 515. If the particular UE is not associated with delay sensitiveservices provided by HSDPA no action is taken in response to the signalreceived in step 511.

In FIG. 5 c, a flow chart illustrating yet some other steps performed ina scheduler, for example a MAC-hs scheduler, adapted to operate inaccordance with the scheduling methods as described herein is shown.Thus, the scheduler 307 can at any time receive a signal from the RNC305 that a particular UE 303 will exit CPM as indicated by step 521.Upon reception of such an exit CPM signal for a particular UE thescheduler will check if that particular UE was reconfigured whenentering CPM, step 523. If the particular UE was reconfigured thescheduler will restore, for example by updating the scheduler prioritycalculation algorithm for that particular UE, the UE to reflect thechanged mode of the UE, step 525. If the particular UE was notreconfigured upon entry into CPM, no action is taken in response to thesignal received in step 521. Of course other events may also trigger thescheduler to update the scheduler priority algorithm applied to aparticular user, the above description serving as an example only.

Using the method and system as described herein will result in asignificantly reduced packet delay and packet loss rate for usersoperating in a system environment having supporting differenttechnologies, such as for example HSDPA users in a CPM supported radionetwork system. The method is easy to be implemented in products and hasa low algorithm complexity. Furthermore there will be no impact onhardware and very small impact on software.

1-22. (canceled)
 23. A method of scheduling users in radio networksystem, characterized by the steps of: for each user in a user groupdetermining a scheduling priority, the scheduling priority beingdependent on a scheduling coefficient representing the unusable time foreach user scheduling the users in accordance with the determinedscheduling priority.
 24. A method according to claim 23, characterizedby the additional step of: re-determining the scheduling priority for auser in response to a changed mode for said user.
 25. A method accordingto claim 23, characterized in that the scheduling priority also isdependent on parameters representing other scheduling coefficients. 26.A method according to claim 25, characterized in that the otherscheduling coefficients include coefficients corresponding to one ormany of the following parameters: maximum delay, average rate,retransmission rate and channel quality indicator (CQI).
 27. A methodaccording to claim 25, when the radio network is a Wideband CodeDivision Multiple Access (WCDMA) network supporting High-Speed DownlinkPacket Access (HSPDA) and ComPressed Mode (CPM), characterized in thatone other scheduling coefficient is a scheduling coefficientcorresponding to a parameter representing the Transmission Gap (TG)pattern for a user in CPM.
 28. A method according to claim 23, when theusers are scheduled in accordance with a maximum delay scheme,characterized in that prior to a transmission gap, during apre-determined time period the unusable Transmission Time Intervals(TTIs) are set as the delay (maximum_Delay):f(maximum_delay)=1/(T_(MAX)−(t _(queue) +T _(unusable))) where t_(queue)is the time corresponding to the time a packet has already been queuedand T_(MAX) is the maximum allowable queuing delay.
 29. A methodaccording to claim 23, when the users are scheduled in accordance with aproportional fair scheduling scheme, characterized in that prior to atransmission gap, during a pre-determined time period the unusableTransmission Time Intervals (TTIs) are set as the used time (t_(used)):${f({average\_ rate})} = \left( \frac{N_{b}}{t_{used} + T_{unusable}} \right)^{- 1}$where t_(used) is a certain period before the scheduling prioritycalculation and N_(b) is the number of transmitted bits during t_(used.)30. A method according to claim 23, when more than one schedulingcoefficient is used to determine the scheduling priority characterizedin that the scheduling priority is determined as a function of all usedscheduling coefficients.
 31. A scheduler for scheduling users in radionetwork system, characterized by: means for determining a schedulingpriority for each user in a user group where said determination meansare adapted to determine the scheduling priority in response ascheduling coefficient representing the unusable time for each user, andmeans for scheduling the users in accordance with the determinedscheduling priority.
 32. A scheduler according to claim 31,characterized by: means for re-determining the scheduling priority for auser in response to a changed mode for said user.
 33. A scheduleraccording to claim 31, characterized in that the means for determining ascheduling priority for each user in a user group are configured todetermine the scheduling priority also in response to schedulingparameters representing additional scheduling coefficients.
 34. Ascheduler according to claim 33, characterized in that the otherscheduling coefficients include coefficients corresponding to one ormany of the following parameters: maximum delay, average rate,retransmission rate and channel quality indicator (CQI).
 35. A scheduleraccording to claim 33, characterized that the means for determining ascheduling priority for each user in a user group are configured todetermine the scheduling priority in response to a schedulingcoefficient corresponding to a parameter representing the TransmissionGap (TG) pattern for a user in ComPressed Mode (CPM).
 36. A scheduleraccording to claim 33 for scheduling users in accordance with a maximumdelay scheme, characterized by means for setting the unusableTransmission Time Intervals (TTIs) as the delay (maximum_Delay)f(maximum_delay)=1/(T _(MAX)−(t _(queue) +T _(unusable))) prior to atransmission gap and during a pre-determined time period where t_(queue)is the time corresponding to the time a packet has already been queuedand T_(MAX) is the maximum allowable queuing delay.
 37. A scheduleraccording to claim 31, for scheduling users in accordance with aproportional fair scheduling scheme, characterized by means for prior toa transmission gap, during a pre-determined time period setting theunusable Transmission Time Intervals (TTIs) are set as:${f({average\_ rate})} = \left( \frac{N_{b}}{t_{used} + T_{unusable}} \right)^{- 1}$where t_(used) is a certain period before the scheduling prioritycalculation and N_(b) is the number of transmitted bits during f_(used).38. A scheduler according to claim 31, characterized by means fordetermining the scheduling priority as a function of all used schedulingcoefficients.